1 files changed, 107 insertions, 0 deletions
diff --git a/u/trace/itrace.ts b/u/trace/itrace.ts
new file mode 100644
index 0000000..e6189d3
--- /dev/null
+++ b/u/trace/itrace.ts
@@ -0,0 +1,107 @@
+import type { Mapper, SideEffect, Supplier } from "@emprespresso/pengueno";
+
+// the "thing" every Trace writer must "trace()"
+type BaseTraceWith = string;
+export type ITraceWith<T> = BaseTraceWith | T;
+export interface ITrace<TraceWith> {
+  addTrace: Mapper<ITraceWith<TraceWith>, ITrace<TraceWith>>;
+  trace: SideEffect<ITraceWith<TraceWith>>;
+}
+
+export type ITraceableTuple<T, TraceWith> = [T, BaseTraceWith | TraceWith];
+export type ITraceableMapper<
+  T,
+  U,
+  TraceWith,
+  W = ITraceable<T, TraceWith>,
+> = (
+  w: W,
+) => U;
+
+export interface ITraceable<T, Trace = BaseTraceWith> {
+  readonly trace: ITrace<Trace>;
+  get: Supplier<T>;
+  move: <U>(u: U) => ITraceable<U, Trace>;
+  map: <U>(
+    mapper: ITraceableMapper<T, U, Trace>,
+  ) => ITraceable<U, Trace>;
+  bimap: <U>(
+    mapper: ITraceableMapper<
+      T,
+      ITraceableTuple<U, Array<Trace> | Trace>,
+      Trace
+    >,
+  ) => ITraceable<U, Trace>;
+  peek: (peek: ITraceableMapper<T, void, Trace>) => ITraceable<T, Trace>;
+  flatMap: <U>(
+    mapper: ITraceableMapper<T, ITraceable<U, Trace>, Trace>,
+  ) => ITraceable<U, Trace>;
+  flatMapAsync<U>(
+    mapper: ITraceableMapper<T, Promise<ITraceable<U, Trace>>, Trace>,
+  ): ITraceable<Promise<U>, Trace>;
+}
+
+export class TraceableImpl<T, TraceWith> implements ITraceable<T, TraceWith> {
+  protected constructor(
+    private readonly item: T,
+    public readonly trace: ITrace<TraceWith>,
+  ) {}
+
+  public map<U>(
+    mapper: ITraceableMapper<T, U, TraceWith>,
+  ) {
+    const result = mapper(this);
+    return new TraceableImpl(result, this.trace);
+  }
+
+  public flatMap<U>(
+    mapper: ITraceableMapper<
+      T,
+      ITraceable<U, TraceWith>,
+      TraceWith
+    >,
+  ): ITraceable<U, TraceWith> {
+    return mapper(this);
+  }
+
+  public flatMapAsync<U>(
+    mapper: ITraceableMapper<
+      T,
+      Promise<ITraceable<U, TraceWith>>,
+      TraceWith
+    >,
+  ): ITraceable<Promise<U>, TraceWith> {
+    return new TraceableImpl(
+      mapper(this).then((t) => t.get()),
+      this.trace,
+    );
+  }
+
+  public peek(peek: ITraceableMapper<T, void, TraceWith>) {
+    peek(this);
+    return this;
+  }
+
+  public move<Tt>(t: Tt): ITraceable<Tt, TraceWith> {
+    return this.map(() => t);
+  }
+
+  public bimap<U>(
+    mapper: ITraceableMapper<
+      T,
+      ITraceableTuple<U, Array<TraceWith> | TraceWith>,
+      TraceWith
+    >,
+  ) {
+    const [item, trace] = mapper(this);
+    const traces = Array.isArray(trace) ? trace : [trace];
+    return new TraceableImpl(
+      item,
+      traces.reduce((trace, _trace) => trace.addTrace(_trace), this.trace),
+    );
+  }
+
+  public get() {
+    return this.item;
+  }
+}